scratch.md (4470B)
1 ---
2 title: .Scratch
3 description: Acts as a "scratchpad" to store and manipulate data.
4 date: 2017-02-01
5 publishdate: 2017-02-01
6 lastmod: 2017-02-01
7 keywords: [iteration]
8 categories: [functions]
9 menu:
10 docs:
11 parent: "functions"
12 toc:
13 signature: []
14 workson: []
15 hugoversion:
16 relatedfuncs: []
17 deprecated: false
18 draft: false
19 aliases: [/extras/scratch/,/doc/scratch/]
20 ---
21
22 Scratch is a Hugo feature designed to conveniently manipulate data in a Go Template world. It is either a Page or Shortcode method for which the resulting data will be attached to the given context, or it can live as a unique instance stored in a variable.
23
24 {{% note %}}
25 Note that Scratch was initially created as a workaround for a [Go template scoping limitation](https://github.com/golang/go/issues/10608) that affected Hugo versions prior to 0.48. For a detailed analysis of `.Scratch` and contextual use cases, see [this blog post](https://regisphilibert.com/blog/2017/04/hugo-scratch-explained-variable/).
26 {{% /note %}}
27
28 ### Contexted `.Scratch` vs. local `newScratch`
29
30 Since Hugo 0.43, there are two different ways of using Scratch:
31
32 #### The Page's `.Scratch`
33
34 `.Scratch` is available as a Page method or a Shortcode method and attaches the "scratched" data to the given page. Either a Page or a Shortcode context is required to use `.Scratch`.
35
36 ```go-html-template
37 {{ .Scratch.Set "greeting" "bonjour" }}
38 {{ range .Pages }}
39 {{ .Scratch.Set "greeting" (print "bonjour" .Title) }}
40 {{ end }}
41 ```
42
43 #### The local `newScratch`
44
45 {{< new-in "0.43" >}} A Scratch instance can also be assigned to any variable using the `newScratch` function. In this case, no Page or Shortcode context is required and the scope of the scratch is only local. The methods detailed below are available from the variable the Scratch instance was assigned to.
46
47 ```go-html-template
48 {{ $data := newScratch }}
49 {{ $data.Set "greeting" "hola" }}
50 ```
51
52 ### Methods
53
54 A Scratch has the following methods:
55
56 {{% note %}}
57 Note that the following examples assume a [local Scratch instance](#the-local-newscratch) has been stored in `$scratch`.
58 {{% /note %}}
59
60 #### .Set
61
62 Set the value of a given key.
63
64 ```go-html-template
65 {{ $scratch.Set "greeting" "Hello" }}
66 ```
67
68 #### .Get
69
70 Get the value of a given key.
71
72 ```go-html-template
73 {{ $scratch.Set "greeting" "Hello" }}
74 ----
75 {{ $scratch.Get "greeting" }} > Hello
76 ```
77
78 #### .Add
79
80 Add a given value to existing value(s) of the given key.
81
82 For single values, `Add` accepts values that support Go's `+` operator. If the first `Add` for a key is an array or slice, the following adds will be appended to that list.
83
84 ```go-html-template
85 {{ $scratch.Add "greetings" "Hello" }}
86 {{ $scratch.Add "greetings" "Welcome" }}
87 ----
88 {{ $scratch.Get "greetings" }} > HelloWelcome
89 ```
90
91 ```go-html-template
92 {{ $scratch.Add "total" 3 }}
93 {{ $scratch.Add "total" 7 }}
94 ----
95 {{ $scratch.Get "total" }} > 10
96 ```
97
98 ```go-html-template
99 {{ $scratch.Add "greetings" (slice "Hello") }}
100 {{ $scratch.Add "greetings" (slice "Welcome" "Cheers") }}
101 ----
102 {{ $scratch.Get "greetings" }} > []interface {}{"Hello", "Welcome", "Cheers"}
103 ```
104
105 #### .SetInMap
106
107 Takes a `key`, `mapKey` and `value` and adds a map of `mapKey` and `value` to the given `key`.
108
109 ```go-html-template
110 {{ $scratch.SetInMap "greetings" "english" "Hello" }}
111 {{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
112 ----
113 {{ $scratch.Get "greetings" }} > map[french:Bonjour english:Hello]
114 ```
115
116 #### .DeleteInMap
117 Takes a `key` and `mapKey` and removes the map of `mapKey` from the given `key`.
118
119 ```go-html-template
120 {{ .Scratch.SetInMap "greetings" "english" "Hello" }}
121 {{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
122 ----
123 {{ .Scratch.DeleteInMap "greetings" "english" }}
124 ----
125 {{ .Scratch.Get "greetings" }} > map[french:Bonjour]
126 ```
127
128 #### .GetSortedMapValues
129
130 Return an array of values from `key` sorted by `mapKey`.
131
132 ```go-html-template
133 {{ $scratch.SetInMap "greetings" "english" "Hello" }}
134 {{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
135 ----
136 {{ $scratch.GetSortedMapValues "greetings" }} > [Hello Bonjour]
137 ```
138
139 #### .Delete
140
141 {{< new-in "0.38" >}} Remove the given key.
142
143 ```go-html-template
144 {{ $scratch.Set "greeting" "Hello" }}
145 ----
146 {{ $scratch.Delete "greeting" }}
147 ```
148
149 #### .Values
150
151 Return the raw backing map. Note that you should only use this method on the locally scoped Scratch instances you obtain via [`newScratch`](#the-local-newscratch), not `.Page.Scratch` etc., as that will lead to concurrency issues.
152
153
154 [pagevars]: /variables/page/